New Phases and Non-Equilibrium Transport in Topological Mesoscopic Superfluids

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NONTECHNICAL SUMMARY This award supports theoretical research on unusual states of matter that appear in liquids and solids when they are confined to very small spatial dimensions. In some special materials, such as superconducting and superfluid condensates, the fundamental particles interact with each other in such a way they move in lockstep, eliminating collisions and forming a new phase of matter that is of great importance to new technologies from lossless electricity transfer to quantum computing. It is possible to increase the complexity of such superfluid phases by confining them to very small regions of space so that the interaction of the superfluid with its confining boundary can lead to the emergence of surface phenomena which could be useful for engineering new phases of matter that are not observed in the bulk material. These new phases of matter have the potential to drive future quantum technologies.In this project, the PI will work with graduate student researchers to develop theoretical and computational tools that will advance the fundamental understanding of the interaction of superconducting phases with their boundaries in confined geometries. The project will provide critical knowledge that will drive the discovery of new boundary-induced surface states in superconductors as well as the development of ways to tune these states to achieve desirable physical properties. The research will bridge past, ongoing, and future experimental work on superfluids in small-scale environments.This project will train graduate students in advanced quantum physics, theoretical and numerical techniques, and complex numerical codes. The PI will also involve undergraduate students in some of the research projects. The PI will continue with his outreach activities at regional schools, where he gives presentations that demonstrate the connections between low-temperature physics, quantum mechanics, and materials to excite students about the possibilities in modern science, and shows them how materials transform our society. TECHNICAL SUMMARY This award supports the theoretical investigation of the fundamental properties of unconventional fermionic condensates in a strongly confined geometry. It aims to build a reliable connection between theory and experiment by creating a set of tools to both rigorously model actual experimental environments, and to supply qualitative analytic descriptions of boundary effects. This project is designed to provide a theoretical link for ongoing experiments on unconventional superconductors and superfluid Helium 3. Analytical and numerical methods, based on the quasi-classical quantum field theory, will be used to obtain realistic spectra of localized Andreev quasiparticle states. One emphasis will be on establishing characteristic signatures of the surface states in multiple experimental probes that include thermodynamic and non-equilibrium responses as well as non-local effects in microscopically confined geometries. The central topics of the research are:1. The PI will explore the effects of boundary conditions, supercurrents, and external fields on the formation of phases with new broken symmetries in multi-component superfluids. 2. The PI will pursue the development of magnetic scattering boundary conditions involving spin-flip dynamics and their effects on surface states in superconductors with entangled spin and orbital degrees of freedom. These studies will include the investigation of spin-current generation in interface regions. 3. Thermal energy transport promises to be a powerful tool to study surface states, including charge-neutral modes of topological materials. The PI will build a theory of surface heat transport by bound states in a confined geometry and domain walls. This project will train graduate students in advanced quantum physics, theoretical and numerical techniques, and complex numerical codes. The PI will also involve undergraduate students in some of the research projects. The PI will continue with his outreach activities at regional schools, where he gives presentations that demonstrate the connections between low-temperature physics, quantum mechanics, and materials to excite students about the possibilities in modern science, and shows them how materials transform our society.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.